1. Field of the Invention
The present invention relates, in general, to a method of connecting thin metallic plate (or plates) by welding along a portion in which a single metallic plate is bent to form a joint portion for welding together or along a joint portion in which two members meet together. In particular, it relates to a method of manufacturing an exhaust pipe of two-passage construction to be used in an exhaust system of an internal combustion engine, as an example of a product manufactured by the above-described method. It also relates to an exhaust pipe of two-passage construction manufactured by the above and other methods, which is free from stress concentration due to pulsations of exhaust gases.
2. Description of Related Art
As a method of welding two relatively thin metallic plates for the purpose of manufacturing a product such as an exhaust pipe of two-passage construction which is suitable for connection to an exhaust manifold of a multi-cylinder internal combustion engine of a motor vehicle, there is known the following method in, for example, Published Unexamined Japanese Patent Application No. 192727/1997 as shown in FIG. 11. Namely, a single piece of metallic plate having a first end and a second end respectively elongated in a longitudinal direction of the exhaust pipe is bent substantially into S shape (i.e., a configuration of an alphabet xe2x80x9cSxe2x80x9d), as seen in cross section. The product thus obtained has: a partition plate or a partition wall xe2x80x9caxe2x80x9d which extends in a diametrical direction and is elongated in a longitudinal direction of the exhaust pipe; and substantially semicircular peripheral wall portions b, b on each lateral side of the partition plate (i.e., on a side at a right angle to the partition plate). In this manner, independent chambers d, d are formed between the partition plate xe2x80x9caxe2x80x9d and the peripheral walls b, b for passing therethrough the exhaust gases from the engine. Diametrical end portions, as seen in cross section, of the first end and the second end of the metallic plate are respectively bent radially inward to form connecting pieces c, c which lie along the partition plate xe2x80x9caxe2x80x9d in its assembled state. Radially outer sides of the connecting pieces c and the partition plate xe2x80x9caxe2x80x9d are welded together from a radially out side to thereby form welding beads e, e. On both longitudinal end portions of this exhaust pipe, flanges are welded for connecting the exhaust pipe to the engine on an upstream side thereof as well as to a catalyst converter on a downstream side thereof.
The exhaust pipe of two-passage construction thus formed has, however, the following disadvantages. Namely, a welding bead e which is formed in the longitudinal direction of the exhaust pipe is likely to protrude beyond the outer circumferential surface of the exhaust pipe. It follows that, when the longitudinal end portion of this welded exhaust pipe is to be inserted into the flange for fixing it to the exhaust pipe by means of welding, or when an outer pipe which is used for covering the inner pipe for the purpose of thermal insulation is swaged (or tapered to a smaller diameter) to thereby bring the two members into close contact with each other, the protruded welding bead e is an obstacle.
As a solution, the following arrangement may be considered as shown in FIG. 12A. The exhaust pipe of two-passage construction in this example is formed into a substantially S shape in cross section with a single piece of relatively thin metallic plate. It is made up of: a central partition plate xe2x80x9caxe2x80x9d which forms, as seen in cross section, a diametrical line of the exhaust pipe and which extends in the longitudinal direction throughout the exhaust pipe; a substantially semicircular peripheral wall b which is formed on each lateral side of the central partition plate xe2x80x9caxe2x80x9d; and a connecting piece cxe2x80x2 which is formed on each end of the metallic plate and which is bent so as to partially overlap with the partition plate xe2x80x9caxe2x80x9d in close contact with each other at each diametrically outer end of the partition plate xe2x80x9ca.xe2x80x9d As a result, on each diametrically outer end portion of the partition plate xe2x80x9caxe2x80x9d, there is provided a groove (or valley) f substantially in the shape of an alphabet V. This groove f is formed by an arched end of the thin metallic plate and that arched end of the semicircular peripheral wall b which transforms (or changes) into the central partition plate xe2x80x9ca.xe2x80x9d Welding is then made at this groove f by means of a welding gun (or a welding torch) g by generating an arc between the welding gun g and a bottom of the groove f in an attempt to integrally weld the central partition plate xe2x80x9caxe2x80x9d and the peripheral wall b. In welding, however, electric discharging is likely to take place toward that portion of the mother material (peripheral wall b) which is closer to the welding gun g as shown by arrows g1, g1. As a result of this electric discharging, a lump h of welded metal (welding bead) is likely to be formed as shown in FIG. 12B in a manner not to reach deep into the groove (or the overlapped portion). A penetration bead is sometimes formed to thereby reduce the strength of the mother material. Sometimes, a penetrating hole i which breaks through the peripheral wall b is formed as shown in FIG. 12C. If an attempt is made to enlarge the width of the groove f, the cross section of the exhaust pipe approaches the shape of a flattened one, resulting in a reduction in the area of flow of the exhaust gases.
The exhaust pipe of two-passage construction as disclosed in the above-described Published Unexamined Japanese Patent Application No. 192727/1997 has still another disadvantage as explained hereinbelow. Namely, when the exhaust gases from the multi-cylinder internal combustion engine pass through a right side passage (as shown in FIG. 11), the central partition plate xe2x80x9caxe2x80x9d tends to deflect toward the left side by the exhaust pressure as shown by dotted lines a1. When the exhaust gases pass through the left side passage d, the central partition plate xe2x80x9caxe2x80x9d tends to deflect toward the right side by the exhaust pressure as shown by dotted lines a2. As a result, by the pulsation of the exhaust gases to pass through the two passages d, d, the partition plate xe2x80x9caxe2x80x9d vibrates by alternately bending in opposite directions as shown by dotted lines a1, a2. This bending takes place with the following point serving as the point of bending, i.e., each welding portion between the connecting piece xe2x80x9ccxe2x80x9d and the partition plate xe2x80x9caxe2x80x9d or a portion which lies on the radially inside thereof. Stresses are concentrated on these points of bending and fatigue occurs there if the vibrations continue.
In view of the above-described points, the present invention has an object of providing a method of connecting two elongated portions of a metallic plate by welding, a method of manufacturing an exhaust pipe of two-passage construction as an example of a product manufactured by the above-described method, as well as an exhaust pipe of two-passage construction manufactured by the above and other methods.
In order to attain the above and other objects, according to one aspect of the present invention, there is provided a method of connecting two elongated portions of a metallic plate, comprising the steps of: longitudinally disposing the two elongated portions at an angle so as to form a groove of substantially V shape in cross section having a substantially closed end and an open end; providing a target elongated along the groove, the target extending from the substantially closed end toward the open end; and generating a welding arc between the target and a welding gun disposed on a side of the open end above the target such that the substantially closed end of the two elongated portions and the target are welded together.
Preferably, the target is formed by bending that end of one of the elongated portions which lies on the substantially closed end toward the open end. The target may be arranged to lie on an inner surface of the other of the elongated portions, or may be formed by an independent target other than the elongated members.
According to this method, welding arc is generated in a manner directed to the target. Therefore, an accurate welding is possible, and thus even a relatively thin metallic plate can be welded without giving rise to the problem that the penetrating hole breaks through the metallic plate.
According to another aspect of the present invention, there is provided a method of manufacturing an exhaust pipe of two-passage construction, comprising the steps of: preparing a metallic plate having a first end and a second end respectively elongated in a longitudinal direction of the exhaust pipe; bending the metallic plate into a substantially S shape in cross section having a diametrically extending central partition plate and a substantially semicircular peripheral wall on each lateral side of the partition plate in such a manner that a groove of substantially V shape in cross section having a substantially closed end on a radially inner side and an open end on a radially outer side is formed at each diametrically outer portion of said partition plate; providing a target elongated along the groove in a manner to extend substantially radially outward from the closed end; and generating a welding arc between the target and a welding gun disposed on a side of the open end such that the substantially closed end and the target are welded together.
Preferably, the target is formed by bending the first end and the second end, respectively, of the metallic plate toward the radially outer end of the partition plate. The target may also be formed by doubly folding a radially outer portion of the partition plate substantially into a U shape such that a closed end of the U shape faces radially outward in the groove. The target may also be formed by providing an independent member other than the metallic plate. The target may still furthermore be arranged to lie on an inner surface, in the groove, of the partition plate.
According to this method, the welding bead can be formed accurately on the closed end of the groove.
According to still another aspect of the present invention, there is provided a method of manufacturing an exhaust pipe of two-passage construction, comprising the steps of: a) bending two longitudinally elongated metallic plates respectively into substantially semicircles with longitudinally elongated sides being further bent radially inward to thereby form inwardly inclined end portions; b) assembling the semicircles obtained in step a) together such that the inclined end portions of one semicircle face corresponding inclined end portions of the other semicircle to thereby form a substantially circular semi-product, the semi-product having on each diametrically opposite sides thereof a groove of substantially V shape in cross section with a substantially closed end on a radially inner side and an open end on a radially outer side; c) interposing a diametrically extending central partition plate along the grooves in a manner to extend diametrically outward from each of the closed ends, whereby a target is formed by a portion extended beyond each of the closed ends; and d) generating a welding arc between the target and a welding gun disposed on a side of the open end such that the substantially closed end and the target are welded together.
According to the above method, an exhaust pipe of two-passage construction can be made not by a single piece of metallic plate but by combining three different pieces of metallic plate.
According to still further aspect of the present invention, there is provided an exhaust pipe of two-passage construction comprising: a central partition plate extending in a diametrical direction and in a longitudinal direction throughout the exhaust pipe; a substantially semicircular peripheral wall on each lateral side of the partition plate so as to extend in the longitudinal direction of the partition plate, the partition plate and each of the peripheral walls jointly forming at each of radially outer portions of the partition plate a groove of substantially V shape in cross section having a substantially closed end on a radially inner side and an open end on the radially outer side; and a target elongated along the groove in a manner to extend substantially radially outward from said substantially closed end of the groove, the target being adapted to be integrally welded with the radially inner side of the groove.
Preferably, the central partition plate and the semicircular walls are formed by one metallic plate and the target is formed by bending each end of the semicircular walls. The target may be formed by doubly folding a diametrically outer portion of the partition plate substantially into a U shape such that a closed end of the U shape faces radially outward in the groove. The target may be formed by providing an independent target member other than the partition plate and the semicircular wall. The target may be arranged to lie along an inner surface, in the groove, of the partition plate, or may be constituted by extending the central partition plate beyond the closed radially inner end of the groove.
According to the above-described arrangement, there can be obtained an exhaust pipe of two-passage construction which is superior in welding quality by making use of the target.
According to a still further aspect of the present invention, there is provided an exhaust pipe of two-passage construction comprising: a central partition plate extending in a diametrical direction and in a longitudinal direction throughout the exhaust pipe; a substantially semicircular wall formed on each lateral side of the partition plate so as to extend in the longitudinal direction of the partition plate; a groove of substantially V shape in cross section formed on each diametrically outer end portion of the partition plate, the groove having a welded portion between the partition plate and a radially inner end of the groove, wherein the welded portion lies radially inward of an imaginary line of an inner circumference of the semicircular wall.
Preferably, the partition plate has a larger bending rigidity at a central portion thereof than at both radially outer portions thereof. The partition plate and the semicircular walls may be formed by a single piece of metallic plate. The central portion of the partition plate may have a larger thickness that the remaining portion of the exhaust pipe. The partition plate may also have a plurality of reinforcing ribs elongated in the diametrical direction of the partition plate, the reinforcing ribs being disposed at a longitudinal distance from each other. The groove preferably satisfies a condition of j/W less than 2, wherein j is a depth from a diametrically outer end of the groove to a connecting portion and W is a maximum width of the groove. Otherwise, the groove of substantially V shape satisfies a condition of L/Dxe2x89xa70.05, wherein D is an imaginary inner diameter of the exhaust pipe and L is a distance from D to a connecting portion.
According to this arrangement, there can be obtained an exhaust pipe of two-passage construction which is less subjected to the stresses due to the pulsations of the exhaust gases. If the groove is formed to satisfy the above conditions, welding becomes easy with a particular kind of welding gun.